Microsoft has revealed that they will announce the next-gen XBox on May 21st.
A Facebook event has been set up as well with the following announcement image including:
A New Generation Revealed. Be part of this historic online event, featuring a live stream, video, images, updates and more.
Dubbed the "XBox 720," it's rumored the new console might be slightly less powerful than the PS4, but have a better capability to do other tasks than gaming (like their new "TV series" programming), might not be backwards compatible; however, an add-on is rumored, and might require users to be "always online."